A mechanical coolant pump is provided with a pump wheel and a rotatable rotor shaft being radially and axially supported by a roller bearing. The outer bearing ring of the roller bearing is normally press-fit into a cylindrical part of the stationary pump frame body. If the mechanical coolant pump is switchable with a friction clutch, another roller bearing is provided to support the rotatable driving wheel. If the driving wheel is directly supported by the stationary pump frame body, the outer ring of the roller bearing is press-fit into a cylindrical part of the pump frame body.
The press-fitting of the outer bearing ring of the roller bearing into a cylindrical part of the pump frame body requires very precisely manufactured cylindrical press-fit surfaces of the corresponding parts. Additionally, the fixing procedure is complicated as well.